Doxycycline : Therapeutic uses, Dosage & Side Effects
Doxycycline is an semisynthetic broad spectrum tetracycline antibiotic. It is used to treat infections caused by bacteria and protozoa.
Dose : 100-200 mg OD
Route : Oral, IV
Onset of action : ?
Plasma Half-life : 18-24 hours
Duration of action : ?
Bioavailability : 100%
Plasma protein binding : 90% (High)
Metabolism : Hepatic
Pregnancy risk category : D
Chemical formula : C22H24N2O8
IUPAC name : (4S,4aR,5S,5aR,6R,12aS)-4-(Dimethylamino)-3,5,10,12,12a-pentahydroxy-6-methyl-1,11-dioxo-1,4,4a,5,5a,6,11,12a-octahydrotetracene-2-carboxamide
Trade name : Tetradox, Biodoxi, Doxi, Novadox, Vibramycin, Acticlate, Adoxa, Alodox, Avidoxy, Doryx, Mondoxyne NL, Monodox, Morgidox, Ocudox Convenience Kit, Oracea, Oraxyl, Targadox, Doxyhexal, Doxylin
Antibacterial spectrum : Doxycycline is active against both gram positive & gram negative bacteria. Moraxella catarrhalis, Brucella melitensis, Chlamydia pneumoniae, and Mycoplasma pneumoniae, Streptococcus, Ureaplasma are generally susceptible to doxycycline, while some Haemophilus spp., Mycoplasma hominis, and Pseudomonas aeruginosa have developed resistance to varying degrees.
Therapeutic uses : Doxycycline is indicated for both protozoal & bacterial infections.
1. Used as Antibacterial drug : Doxycycline is indicated for treatment of following infectins caused by susceptible strains of bacteria :
- Rocky Mountain spotted fever, typhus fever, Q fever, rickettsialpox, and tick fevers
- Respiratory tract infections caused by Mycoplasma pneumoniae
- Lymphogranuloma venereum, trachoma, inclusion conjunctivitis, and uncomplicated urethral, endocervical, or rectal infections in adults caused by Chlamydia trachomatis
- Psittacosis (ornithosis) caused by Chlamydia psittaci
- Brucellosis caused by Brucella species (in conjunction with streptomycin)
- Bartonellosis caused by Bartonella bacilliformis
- Granuloma inguinale caused by Calymmatobacterium granulomatis
- Lyme disease caused by Borrelia burgdorferi
- Nongonococcal urethritis caused by Ureaplasma urealyticum
- Relapsing fever due to Borrelia recurrentis
- Chancroid caused by Haemophilus ducreyi
- Plague due to Yersinia pestis
- Tularemia due to Francisella tularensis
- Cholera caused by Vibrio cholerae
- Campylobacter fetus infections
- Severe acne (adjunctive therapy)
When penicillin is contraindicated in a patient, doxycycline can be used to treat following infections :
- Syphilis caused by Treponema pallidum
- Yaws caused by Treponema pertenue
- Listeriosis due to Listeria monocytogenes
- Vincent’s infection caused by Fusobacterium fusiforme
- Actinomycosis caused by Actinomyces israelii
- Infections caused by Clostridium species
Doxycycline can also be used to treat following infections but only when bacteriologic testing indicates appropriate susceptibility to the drug :
- E. coli infections
- Enterobacter aerogenes infections
- Shigella species infections
- Acinetobacter species infections
- Respiratory tract infections caused by Haemophilus influenzae, Streptococcus pneumoniae, Klebsiella species
- Urinary tract infections caused by Klebsiella species
- Skin and soft tissue infections caused by Staph. aureus, including methicillin-resistant Staph. aureus infections
- Anthrax caused by Bacillus anthracis infection
2. Used as Antiprotozoal drug : It is used in prophylaxis against malaria. It can be used in a treatment plan in combination with other agents (such as quinine) but should not be used alone for initial treatment of malaria, even when the parasite is doxycycline-sensitive, because the antimalarial effect of doxycycline is delayed. This delay is related to its mechanism of action, which is to specifically impair the progeny of the apicoplast genes, resulting in their abnormal cell division.
3. Used as Antihelminthic drug : Doxycycline kills the symbiotic Wolbachia bacteria in the reproductive tracts of parasitic filarial helminth, making the nematodes sterile, and thus reducing transmission of diseases such as elephantiasis.
Mechanism of action : Tetracyclines enter susceptible organisms via passive diffusion & by an energy-dependent transport protein mechanism unique to the bacterial inner cytoplasmic membrane. Tetracyclines concentrate intracellularly in susceptible organisms. The drugs bind reversibly to the 30S subunit of the bacterial ribosome. This action prevents binding of aminoacyl-t-RNA to the mRNA–ribosome complex, thereby inhibiting bacterial protein synthesis.
Side effects : Tetracycline can cause following side effects :
- Irritative effects : Epigastric pain, nausea, vomiting, diarrhoea. The irritative diarrhoea is to be distinguished from that due to superinfection.
- Thrombophlebitis of the injected vein.
- A reversible Fancony syndrome like condition is produced by outdated tetracyclines due to proximal tubular damage caused by degraded products-epitetracycline, anhydrotetracycline and epianhydrotetracycline. Exposure to acidic pH, moisture and heat favours such degradation.
- Phototoxicity (Distortion of nails occurs occasionally)
- Antianabolic effect : Reduce protein synthesis and cause an overall catabolic effect. It induces negative nitrogen balance and can increase blood urea.
- Increased intracranial pressure is noted insome infants.
- Hypersensitivity reactions (infrequent) : Skin rashes, urticaria, glossitis, pruritus ani and vulvae, even exfoliative dermatitis have been reported. Complete cross sensitization is exhibited by different tetracyclines.
- Superinfection : Tetracyclines are the most common antibiotics responsible for superinfections, because they cause marked suppression of the resident flora.
- Teeth and bones : Tetracyclines have chelating property. Calcium-tetracycline chelate gets deposited in developing teeth and bone. Given from midpregnancy to 5 months of extrauterine life, the deciduous teeth are affected: brown discolouration, ill-formed teeth, more susceptible to caries. Tetracyclines given between 3 months and 6 years of age affect the crown of permanent anterior dentition. Repeated courses are more damaging.
Given during late pregnancy or childhood, tetracyclines can cause temporary suppression of bone growth. The ultimate effect on stature is mostly insignificant, but deformities and reduction in height are a possibility with prolonged use.
Drug Interactions : Doxycycline may interact with following drugs :
- Dairy, calcium supplements, iron products, and laxatives containing Mg : Decrease in doxycycline’s effectiveness.
- Antacids : Decrease in doxycycline’s effectiveness.
- Contraindicated in patients who are allergic to antibiotics of tetracycline group.
- It should not be used in pregnant or breast-feeding women or in children less than 8 years of age.
For detailed query or in case of uncertainty, Always consult your doctor or pharmacist.